1. Field of the Invention
The present invention relates to a wiring board having solder bumps therein and to a method for manufacturing the same.
2. Description of Related Art
A conventional wiring board (semiconductor package) has solder bumps formed on pads that are used for mounting an electronic component. Such wiring board includes various types, such as a ball grid array (BGA) and a pin grid array (PGA). On these wiring boards, an electronic component is mounted by flip chip connection in high density through the solder bumps. In addition, the solder bumps are formed by, for example, printing, solder balls or the like. The printing method is a method for forming solder bumps by reflow after printing soldering paste on pads that are formed on a top surface of the wiring board using a metal mask with a plurality of openings. The solder ball method is a method for forming solder bumps by reflow after providing the solder balls on the pads. In addition, in this type of wiring board, a solder resist is formed so as to cover the top surface of the wiring board. The solder resist is provided with a plurality of openings to which the pads are exposed.
Although a diameter of each opening in the solder resist is the same, it might be different depending on a specification of the wiring board. In the printing method, a diameter of an opening of the metal mask can be altered according to the opening of the solder resist to form the solder bumps. However, since the printing method has a disadvantage that the formation of solder bumps is difficult when a pitch between the solder bumps is narrow, the various conventional technologies suggest the solder ball method (e.g., refer to Japanese Patent Application Laid-Open (kokai) No. 2007-281369 (FIGS. 2A to 2K etc.) (the “'369 application”)). In the conventional technology according to the '369 application, a solder resist in which first openings and second openings having a diameter larger than that of the first openings are formed. First solder balls are disposed in the first openings and second solder balls with particle size larger than that of the first solder ball are disposed in the second openings.
However, the conventional technology according to the '369 application requires a process to position first solder balls in first openings while a first mask covering second openings is disposed on a solder resist, and a process to position second solder balls in second openings while a second mask covering the first openings is disposed on the solder resist. As a result, the number of the required loads for forming the solder bumps increases, thereby raising manufacturing costs of the wiring board. Further, the conventional technology according to the '369 application uses two types of solder balls each having a different diameter so as to correspond to two types of openings of the solder resist, each of which has a different diameter. In this respect, variations arise in the height of each solder bump. As a result, a faulty connection is likely to occur between a wiring board and an electronic component.